In this study, we establish a theoretical model of pulse compression and focusing process in an ultrahigh peak power laser system and simulate the dispersion process of parallel grating pair compressor and the focusing process of parabolic mirror based on ray-tracing method and Fraunhofer far-field diffraction. The wavefront distortion for a square diameter is described using the Square-Radial polynomial. The effect of four different wavefront distortions in near-field on the far-field spatio-temporal distribution is analyzed, and the error tolerance is provided under different conditions.